@taricha said:
"I used a LaMotte QAC
titration kit. The indicator gives the "quat" response to both AlgaeFix and Vibrant, but the titration step does not work because precipitate forms instead. So I did analysis of the color change from the quat indicator solution to see if I could find a nice dose-response relationship to AlgaeFix and/or Vibrant."
1. Why did a precipitate form?
2. Is the test designed for use in salt water?
3. This test measures up to 500 ppm. A one percent solution is 10,000 ppm. A 4.5 percent solution is 45,000 ppm.
I apologize - I do not think you're doing the testing completely properly. I do think you're doing the best you can. I fully believe there is QAC in Vibrant at some concentration - I do not believe that the tests done prove that the concentration is the same/similar - nor the same compound.